328 TRANSFORMATION OF ARSENIC INTO A SOLID HYDRIDE. 
when the nitric acid is mixed in very minute proportions 
with other acids, so that we may avail ourselves of the re¬ 
action to detect the least trace of a nitrous compound in 
sulphuric, hydrochloric, or other acids. When once formed, 
however, the solid hydride of arsenic is insoluble in the cold, 
in sulphuric and hydrochloric acid, whether concentrated or 
diluted, and therefore gives no trace of the gaseous hydride 
in Marsh’s apparatus. Of this fact I have repeatedly 
assured myself by placing in the apparatus strips of zinc 
previously coated with the hydride in question. 
For the production of this solid hydride to take place, 
however, the author states that the absence of all other 
metals from the solution is necessary. And not only this; 
the presence in the liquid of certain organic matters, such as 
sugar, gum, gelatine, alcohol, ether, even in small propor¬ 
tion, prevents the formation of the hydride. Nevertheless, 
he adds, the property possessed by arsenic of depositing 
itself on zinc as a hydride in the presence of nitrous com¬ 
pounds affords us the means, if not of isolating, at least of 
characterising it. If arseniuretted hydrogen is passed into 
nitrate of silver, as in Lassaigne’s test, and the excess of 
silver is precipitated by chloride of sodium, the clear liquor 
obtained by filtration, acidulated with a few drops of nitric 
acid, will quickly deposit the hydride on a strip of pure zinc. 
The author affirms that this reaction is second to none in 
sensibility. 
Hitherto sulphuric and hydrochloric acids have been con¬ 
sidered sufficiently pure for toxicological researches when 
proved to be free from arsenic; but the author’s results show 
that it is equally important to have these acids free from 
nitrous compounds. Another source of error exists when 
animal matters suspected to contain arsenic are carbonized 
by a mixture of sulphuric and nitric acids. If the whole of 
the nitric acid is not got rid of, there is the danger that 
when the liquid obtained is tested by Marsh’s method the 
whole of the arsenic may pass into the solid hydride and 
remain undetected .—Condensed from Annales de Chimie et de 
Physique . 
